Analysis: Tokyo water ‘not unsafe’ despite radiation levels

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The notion that safe radiation levels have been exceeded in Tokyo tap water
may sound frightening, but it does not mean that the city’s water is unsafe.

While any increase in radiation exposure will slightly raise the risk of
cancer, particularly thyroid cancer when the isotope iodine-131 is involved,
allowable levels are set extremely conservatively, well below the threshold
at which harm becomes likely.

“What are sometimes called safe doses are several orders of magnitude below
the level at which we know harm begins,” said Professor Malcolm Sperrin,
director of medical physics at the Royal Berkshire Hospital in Reading. “To